1. Field of the Invention
This invention relates to a method and apparatus for determining optical properties of light scattering material for use in various industries including materials, brewing, biomaterials, food, medicine and pharmaceuticals, and in the medical diagnostic field.
2. Description of the Prior Art
There are times when it is necessary to determine the optical properties of light scattering materials in order to establish the composition of slimes and fermentation suspensions in the brewing industry, of cosmetics, foodstuffs and non-transparent materials in the materials industry, and, in the pharmaceuticals and medical supplies industry, of non-transparent liquid products, creams and other semi-solid products as well as biological samples and solid products that can be sampled by crushing, cutting or slicing. A conventional way of determining the optical properties of a scattering body, when the target sample is large enough to be assumed to be an infinite medium or semi-infinite slab, with respect to light propagation, is to determine the equivalent scattering coefficient .mu.s' and absorption coefficient .mu.a of the sample by comparing the results of a time resolved determination and a theoretical analytical solution ("Determination of tissue optical parameters by time resolved analysis," Tsunazawa et al., 34th meeting of the Japan ME Society (1995)).
That method of determining optical properties is effective with respect to samples large enough to be assumed to be an infinite medium or semi-infinite slab or samples with a special geometrical shape such as a sphere or a cylinder. However, it cannot be used to quantify the optical properties of samples that are too small to apply an analytical solution to, such as samples that are too small to be assumed to be an infinite medium or semi-infinite slab and present many problems with respect to determining optical properties by the least squares method, and samples having an arbitrary shape. It also cannot be applied to samples having a distribution of optical properties.
In such cases optical properties can be determined by the Monte Carlo method, or finite-element method or other method of numerical analysis. However, the time required to perform the numerical calculations makes it difficult to implement the Monte Carlo or finite-element methods at the time of the analysis. One way of resolving this problem is to prepare a look-up table beforehand using a series of calculations based on the Monte Carlo method or numerical analyses, for a large number of conditions, and referring to this table during the analysis.
Thus, there has been a need for a way of readily determining optical properties of samples, even small or arbitrarily-shaped samples, or samples in which there is a distribution of optical properties.
An object of the present invention is to provide a method and apparatus for determining optical properties of light scattering material, even when a sample is too small to be assumed to be an infinite medium or semi-infinite slab with respect to light propagation, or is of an arbitrary shape, or has a distribution of optical properties.